A blast furnace functions optimally when the charge drops in a uniform manner and when the consumption of fuel is reduced to a minimum. These two conditions are a function on one hand of the distribution of reducing gases through the charge and on the other hand of the optimal exploitation of their reducing power.
In order to be able to maximize the exploitation of the reducing power of the gases, it is necessary to known at all times the chemical makeup of the gaseous phase which is immediately above the charge. Thus for instance knowing the fact that CO is being liberated mainly at the center of the top of the charge means something significant to the person skilled in the art which will lead him to intervene by changing the distribution of the materials in the furnace, according to their degree of reducibility, in the region of the top of the charge. For instance material (e.g. ore) to be reduced would be concentrated in a location where the reducing power was considerable, as where considerable H.sub.2, CO, and CH.sub.4 and relatively little CO.sub.2 was being liberated.
It is known to determine the chemical profile of the gaseous phase on top of the charge by using mobile probes to extract samples of the gas whose makeup is determined by an appropriate analysis technique. There are in effect special probes conceived to sweep as intensely as possible the area above the top of the charge. Thus these probes are exposed to high temperatures as well as to mechanical stresses. The described analysis procedure takes place in steps, so that the number of samplings, which is as high as usefully possible, determines the accuracy of the result obtained.
Considerable progress have been made toward increasing the speed and the number of detection points by a process which provides for measuring the infrared radiation and thereby determining the thermal profile at the top of the charge and for correlating the temperature measured at a given location with the composition of the gases at this location. This is done with the aid of standard calibration graphs, for example by a method similar to that which has been described above. In any case this infrared analysis technique is only an indirect method in the present context and the correlation between the readings taken and the information wanted is not unequivocal, so much that the results obtained by this procedure are not reliable enough to permit the metallurgist to intervene effectively.